The present invention generally relates to a signal processor and a method for processing a receiving signal, particularly to a broadband dual receiver with dual conversion and low intermediate frequency.
Nowadays, it is desirable or necessitated, respectively, in many applications that several usable frequency bands are received at the same time. For example, in the field of satellite-aided positioning it is useful to evaluate signals in two usable frequency ranges spaced apart from each other for improving spatial resolution. Apart from this, in the field of mobile communication it is, also sometimes desirable to receive and evaluate signals in two different frequency bands simultaneously or alternatively.
Dual receivers allow simultaneous reception of two different bands by a single receiver, which saves power consumption and costs.
In currently used receivers for the above-described applications, for example for simultaneously receiving two bands in a satellite-aided navigation system, there are two different groups: very broadband receivers and relatively narrowband dual receivers. Both of them are high-precision receivers for high-end navigating and positioning systems.
In the first type of receivers, high precision (for example with regard to positioning) is obtained by the large bandwidth of the transmission method DSSS (direct-sequence spread spectrum). For example, a bandwidth in a range from 20 MHz up to 70 MHz or more is used. Processing such a high bandwidth is a great challenge for the receiver. A high bandwidth mainly affects filtering and group run-time changes in a pass range of the filters, a cutoff frequency of a variable gain amplifier (also referred to as VGA) and a sampling rate of an analog/digital converter (also referred to as ADC). Based on the high necessitated bandwidth or the high cutoff frequency, respectively, for example, an anti-alias filter (which is, for example, upstream of the analog/digital converter) is implemented in a passive manner. The variable gain amplifier (VGA) and the analog/digital converter (ADC) consume a comparatively high amount of current (due to the high signal bandwidth to be processed).
In a second type of receivers, high precision is obtained by simultaneously receiving two bands or frequency bands, respectively. By this method, among other things, an ionospheric group run-time change (representing a negative influence variable in a navigation system or satellite-based positioning system) is compensated by measuring two delays from two different carrier frequencies. However, receiver architectures conventionally used for receiving two frequency bands have, like broadband receivers, a comparatively complex circuit structure and comparatively high current consumption.